We have a row of autumn bliss in the garden (about 8 years old now I should think) which produced a large summer crop as well as a smaller autumn one in their third year. After mentioning this to the old boy next door he informed me that it was because I hadn't cut them back properly in the spring (general laziness and a wet start to the year I should imagine!) and that autumn rasberries fruit off new stems and should be cut to the ground the following spring. If you don't they fruit again (summer rasberries on year old stems so you only prune the stems which have fruited) the following summer but you won't get as much in the autumn. A good compromise if you only have 1 variety is to thin the stems in the autumn so that you get some fruit in the summer and some more in the autumn which is about right for us and the number of canes we have - think we had 6 canes originally, bought as part of a "fruit orchard" set from the garden centre.